The present invention relates to methods for forming and maintaining precise cavity dimensions. More specifically, but without limitation thereto, the present invention relates to a method for forming a uniform cavity between the electrode substrates of a nematic liquid crystal display (LCD) and a device made by this method.
A simplified structure of a liquid crystal display is illustrated in FIG. 1. To provide accurate control of the electrical field and optical path length between transparent electrode substrates 102, it is desirable to maintain a uniform spacing "d" in the cavity between electrode substrates 102 filled with a liquid crystal material 106. Current methods for establishing spacing "d" depend on the flatness of electrode substrates 102.
In the top and side views of a typical liquid display 20 illustrated respectively in FIGS. 2(a) and 2(b), spacer materials 220 made of, for example, chopped glass fibers and micro-plastic balls are typically scattered over the surface of a lower electrode substrate 202. A display area 206 is bordered by an adhesive 200 printed on upper electrode substrate 204 or lower electrode substrate 202. A filling gap 250 may be left for introducing a liquid crystal material (not shown). A pattern of vertical data electrodes 210 on upper electrode substrate 204 opposes a pattern of horizontal scanning electrodes 208 on lower electrode substrate 202 to define pixels within display area 206.
A disadvantage of using scattered glass fibers or micro-plastic balls to define the spacing between data electrodes 210 and scanning electrodes 208 is that the difficulty of maintaining a high degree of flatness increases with the area of the display. This disadvantage is further compounded by the thermal stress of the methods used to bond electrode substrates 202 and 204 with adhesives having different temperature coefficients.
Another disadvantage of this arrangement is that irregularities in the flatness of one or both substrates causes the cavity formed between electrode substrates 202 and 204 to vary in thickness at the electrode gaps. In non-linear active matrix displays, such as ferroelectric LCD's, surface plasmon displays and the like, there is often a critical electric field required to switch the array elements Since the operating voltage is determined by the product of the electric field and the distance between electrodes, a variation in the electrode gaps raises the voltage required to control the array of pixel elements. Other flat panel display technologies including field emission, miniaturized CRT, plasma, micro-electro-mechanical and the like may also benefit from a method for forming a uniform cavity.